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\usepackage{booktabs}
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\begin{document}
\begin{table}[t]
\centering
\begin{tabular}{l ccc}
\toprule \toprule
 & \multicolumn{3}{c}{\bf{Panel A: Speakers}} \\[2mm]
 & Before & During & After \\
\midrule
 Hits & 42.94 & 315.31 & 42.92\\
 & (61.00) & (502.41) & (88.32) \\[2mm]
\midrule
 Difference & -272.37 &  & -272.39\\
 P-value & 0.00 &  & 0.00\\
 N &  86 & 113 &  98 \\
\midrule\midrule
 & \multicolumn{3}{c}{\bf{Panel B: Minority Leaders}} \\[2mm]
 Hits & 23.75 & 139.67 & 47.74\\
 & (31.96) & (106.14) & (75.72) \\[2mm]
\midrule
 Difference & -115.92 &  & -91.93\\
 P-value & 0.00 &  & 0.00\\
 N &  20 &  30 &  23 \\
\bottomrule \bottomrule
\multicolumn{4}{p{.4\textwidth}}{Standard deviations are reported in parentheses. The pre and post-Speaker 
 periods are based on 5 years before and after the Speaker term. }\\
\end{tabular}
\end{table}
\end{document}
